The present invention relates to a boring bar, a process for the production of a boring bar, and the use of such a boring bar for the damping of vibrations during internal turning.
Turning operations can be divided into those for external turning and those for inner turning, the latter normally called internal turning. As the names indicate, external turning operations relate to turning on an external rotating surface of a workpiece, while internal turning refers to turning on an inner rotating surface. A special case of external turning is face turning.
During external turning, the overhang of the tool is not influenced by the length of the workpiece since external rotating surfaces usually are exposed and freely accessible. Thus, dimensions of tool holders may be chosen so that they resist the forces or stresses that arise. However, during internal turning the choice of tool is restricted by the appearance of the workpiece, since this turning operation is usually applied in pre-drilled holes or holes in cast, forged or extruded elements. Thus, when turning in a deep hole, a long boring bar with a long overhang is required, which of course increases the risk of deflection and vibrations, which in turn results in a worse surface smoothness and disturbing noise. This problem is accentuated by the fact that internal turning operations are mainly used for applications with high demands on dimension tolerances and surface smoothness.
Thus, at internal turning the depth of the hole will determine the smallest practically possible overhang. For a larger boring bar diameter (D) the stability is increased, but also here the possibilities are restricted by the fact that the space which is offered by the hole diameter of the workpiece must be respected. By the special circumstances that are present for long overhangs (L) and a restricted bar diameter, the stability is described starting off from the relation L/D. The smaller the relation L/D, the better stability is achieved.
The restrictions concerning the stability for internal turning require that special care must be taken for production planning and preparation. With knowledge of how the shearing forces are influenced by tool geometry and selected cutting data, and how different types of boring bars and tool joints influence stability, deflections and vibrations can to some extent be minimized. However, it would be desirable to reduce them further.
In for instance SE-B-385 797 (and U.S. Pat. No. 3,838,936), a damping arrangement is disclosed for inter alia boring bars, which comprises a damping portion being arranged in an axial boring in the boring bar and being coupled to the same via one or several springing elements in the form of, e.g., sheets or circumferential rings of a resilient material such as rubber. Possibly, a fluidum may be introduced into the space between the damping portion and the boring, in order to contribute to the damping effect. Although this construction certainly reduces vibrations, it is complicated and space-demanding.
Thus, a primary object of the present invention is to provide a boring bar with a reduced tendency for vibrations.
A second object of the present invention is to make possible longer overhangs without thereby increasing the tendency for vibrations.
Still another object of the present invention is to minimize the risk of vibrations in boring bars with the simplest possible construction.